Flooded compressor with improved oil reclamation

Abstract

Oil reclamation for a flooded screw type compressor is improved by replacing the normal distillation still with a refrigerant vaporizer made from a small diameter pipe conduit and a low temperature heat source such as heat tracing. The system purifies lubricating oil of refrigerant by boiling small batches of collected lubricating oil from the bottom of the chiller. Using a small volume for vaporization of the refrigerant allows a low temperature heat source to effectively vaporize the refrigerant from the circulating lubricating oil without complicated systems for control or pumping. A particular form of the vaporizer is simply a small diameter pipe surrounded by heat tracing tape.

What is claimed: 
     
       1. A system for recovering trace amounts of lubricating oil from the refrigerant in a refrigerant system that uses a flooded screw compressor, said system comprising: a) a flooded screw compressor for receiving a vaporized refrigerant and compressing the refrigerant to produce a compressed refrigerant having a liquid phase and containing lubricating oil;   b) passing the compressed refrigerant to an oil separator and separating a lubricant oil stream and separated refrigerant stream from said compressed refrigerant and returning said lubricant oil stream to said compressor;   c) passing said compressed refrigerant to a chiller and vaporizing said refrigerant in said chiller to produce said vaporized refrigerant for return to said compressor;   d) collecting a mixture of liquid refrigerant and oil from said chiller and retaining said mixture in a refrigerant vaporizer having a restricted volume and a low temperature indirect heat input that cannot exceed the vaporization temperature of the lubricating oil;   e) heating said mixture in said refrigerant vaporizer until substantially all of the refrigerant has vaporized to produce a reclaimed oil stream; and   f) returning the reclaimed oil stream from the vaporizer to the compressor.   
     
     
       2. The system of claim 1 wherein said mixture is recovered from the bottom of said chiller. 
     
     
       3. The system of claim 1 wherein said refrigerant vaporizer comprises a length of pipe having a diameter of less than 3 inches and length of less than 18 inches. 
     
     
       4. The system of claim 1 wherein said low temperature heat input comprises electrical heat tracing tape. 
     
     
       5. The system of claim 1 wherein the maximum temperature of said low temperature heat input does not exceed 140° F. 
     
     
       6. The system of claim 1 wherein said refrigerant vaporizer comprises a multiplicity of vertically oriented pipe having a diameter of less than 2 inches and a length of less than 18 inches. 
     
     
       7. The system of claim 1 wherein said mixture is transferred to said refrigerant vaporizer by opening an inlet valve located upstream of said vaporizer, wherein the reclaimed oil passes out of the vaporizer through an outlet valve, vaporized refrigerant is passed back to said chiller by an equalization line located downstream of said inlet valve, and wherein the inlet valve and outlet valve are cycled such that a batch of the liquid mixture enters the vaporizer while the inlet valve is open and the outlet valve is shut, the mixture is vaporized and returned to the chiller via the equalization line while the inlet and outlet valves are shut, and the outlet valve opens while the inlet valve remains shut to return the reclaimed oil to the compressor once a temperature sensor indicates that the temperature in the vaporizer is sufficient to have vaporized all of the refrigerant. 
     
     
       8. The system of claim 1 wherein the low temperature indirect heat input is supplied by a vertical heat exchanger. 
     
     
       9. The system of claim 8 wherein the vertical heat exchanger heats the liquid mixture by indirect heat exchange with lubricant oil from the oil separator. 
     
     
       10. The system of claim 1 wherein said chiller and vaporizer are elevated above said compressor by a sufficient distance to pass the reclaimed oil stream back to the compressor under gravity flow. 
     
     
       11. The system of claim 1 wherein the vaporization of the refrigerant in the refrigerant vaporizer provides sufficient pressure to pass the reclaimed oil stream back to the compressor. 
     
     
       12. A system for recovering trace amounts of lubricating from the refrigerant in a refrigerant system that uses a flooded screw compressor, said system comprising: a) a flooded screw compressor for receiving a vaporized refrigerant and compressing the refrigerant to produce a compressed refrigerant having a liquid phase and containing lubricating oil;   b) passing the compressed refrigerant to an oil separator and separating a lubricant oil stream and separated refrigerant stream from said compressed refrigerant and returning said lubricant oil stream to said compressor;   c) passing said compressed refrigerant to a chiller and vaporizing said refrigerant in said chiller to produce said vaporized refrigerant for return to said compressor;   d) collecting a mixture of liquid refrigerant and oil from said chiller and retaining said mixture in a refrigerant vaporizer comprising at least one vertical conduit having a diameter of less than three inches and length of less than 18 inches to produce a restricted volume and heating the restricted volume with heat tracing around the conduit;   e) heating said mixture in said refrigerant vaporizer until substantially all of the refrigerant has vaporized to produce a reclaimed oil stream; and   f) returning the reclaimed oil stream from the vaporizer to the compressor.   
     
     
       13. The system of claim 11 wherein said mixture is recovered from the bottom of said chiller. 
     
     
       14. The system of claim 11 wherein said refrigerant vaporizes comprises a multiplicity of vertically oriented pipe having a diameter of less than 2 inches. 
     
     
       15. The system of claim 11 wherein said mixture is transferred to said refrigerant vaporizer by opening an inlet valve located upstream of said vaporizer, wherein the reclaimed oil passes out of the vaporizer through an outlet valve, vaporized refrigerant is passed back to said chiller by an equalization line located downstream of said inlet valve, and wherein the inlet valve and outlet valve are cycled such that a batch of the liquid mixture enters the vaporizer while the inlet valve is open and the outlet valve is shut, the mixture is vaporized and returned to the chiller via the equalization line while the inlet and outlet valves are shut, and the outlet valve opens while the inlet valve remains shut to return the reclaimed oil to the compressor once a temperature sensor indicates that the temperature in the vaporizer is sufficient to have vaporized all of the refrigerant. 
     
     
       16. The system of claim 11 wherein said chiller and vaporizer are elevated above said compressor by a sufficient distance to pass the reclaimed oil stream back to the compressor under gravity flow. 
     
     
       17. The system of claim 16 wherein said mixture is transferred to said refrigerant vaporizer by opening an inlet valve located upstream of said vaporizer, wherein the reclaimed oil passes out of the vaporizer through an outlet valve, vaporized refrigerant is passed back to said chiller by an equalization line located downstream of said inlet valve, and wherein the inlet valve and outlet valve are cycled such that a batch of the liquid mixture enters the vaporizer while the inlet valve is open and the outlet valve is shut, the mixture is vaporized and returned to the chiller via the equalization line while the inlet and outlet valves are shut, and the outlet valve opens while the inlet valve remains shut to return the reclaimed oil to the compressor once a temperature sensor indicates that the temperature of the lubricating oil stream leaving the exchanger is sufficient to have vaporized all of the refrigerant. 
     
     
       18. The system of claim 16 wherein the said heat exchange is carried out in a vertical heat exchanger. 
     
     
       19. The system of claim 16 wherein said chiller and vaporizer are elevated above said compressor by a sufficient distance to pass the reclaimed oil stream back to the compressor under gravity flow.